Effects of hemoglobin concentration on deformability of individual sickle cells after deoxygenation

To assess the role of intracellular hemoglobin concentration in the deformability of sickle (HbSS) cells after deoxygenation, rheologic coefficients (static rigidity E and dynamic rigidity eta) of density- fractionated individual sickle erythrocytes (SS cells) were determined as a function of oxygen tension (pO2) using the micropipette technique in a newly developed experimental chamber. With stepwise deoxygenation, E and eta values showed no significant increase before morphologic sickling but rose sharply after sickling. In denser cells, continued deoxygenation led to steep rises of E and eta toward infinity, as the cell behaved as a solid. The pO2 levels at which rheologic and morphologic changes occurred for individual SS cells during deoxygenation varied directly with the cell density. The extent of recovery in E and eta during reoxygenation varied inversely with the cell density. These results provide direct evidence that the intracellular sickle hemoglobin (HbS) concentration of SS cells plays an important role in their rheologic heterogeneity in deoxygenation and reoxygenation. The elevations of eta during pO2 alteration were greater than those of E, especially for the denser cells, suggesting the importance of the elevated dynamic rigidity in initiating microcirculatory disturbances in sickle cell disease.     

Bepridil protects sickle cells against the adverse rheological effects of cyclical deoxygenation

Calcium influx into sickle cells, with consequential activation of the Ca2(+)-activated K+ efflux (Gardos) channel, is a potential cause of cellular dehydration and loss of deformability. Bepridil, a recently described inhibitor of the Gardos channel, was found at pharmacological concentration (1 mumol/l) to inhibit significantly (P less than 0.01) the loss of deformability when sickle cells were subjected to cycles of oxygenation-deoxygenation for 15 h at 37 degrees C. Bepridil also inhibited significantly (P less than 0.005) the formation of irreversibly sickled cells. Drugs that preserve the K+ and therefore water content of erythrocytes are of potential value for hydrotherapy of sickle cell disease.     

Substituted benzaldehydes (12C79 and 589C80) that stabilize oxyhaemoglobin also protect sickle cells against calcium-mediated dehydration

Reversibly sickled cells from patients with homozygous sickle-cell disease were prepared by Percoll-Isopaque density gradient separation and subjected to 15 h of cyclical deoxygenation-reoxygenation in the presence of Ca. After 15 h the sickle cells became dehydrated, losing volume secondary to K efflux via the Ca-activated (Gardos) channel, and showed impaired filterability through 5 microns diameter pores. The substituted benzaldehydes 12C79 and 589C80, which stabilize the oxy-conformation of sickle haemoglobin, showed an additional protective effect at pharmacological concentration by maintaining the K concentration, mean cell volume, and deformability of sickle cells. Drugs that increase the oxygen affinity of sickle haemoglobin may be more effective than specific inhibitors of Ca entry or K efflux in preserving the cation homeostasis and deformability of sickle cells during sickling in vivo.     

Rate of deoxygenation modulates rheologic behavior of sickle red blood cells at a given mean corpuscular hemoglobin concentration

Although the mean corpuscular hemoglobin concentration (MCHC) plays a dominant role in the rheologic behavior of deoxygenated density-defined sickle red blood cells (SS RBCs), previous studies have not explored the relationship between the rate of deoxygenation and the bulk viscosity of SS RBCs at a given MCHC. In the present study, we have subjected density-defined SS classes (i.e., medium-density SS4 and dense SS5 discocytes) to varying deoxygenation rates. This approach has allowed us to minimize the effects of SS RBC heterogeneity and investigate the effect of deoxygenation rates at a given MCHC. The results show that the percentages of granular cells, classic sickle cells and holly leaf forms in deoxygenated samples are significantly influenced by the rate of deoxygenation and the MCHC of a given discocyte subpopulation. Increasing the deoxygenation rate using high K+ medium (pH 6.8), results in a greater percentage of granular cells in SS4 suspensions, accompanied by a pronounced increase in the bulk viscosity of these cells compared with gradually deoxygenated samples (mainly classic sickle cells and holly leaf forms). The effect of MCHC becomes apparent when SS5 dense cells are subjected to varying deoxygenation rates. At a given deoxygenation rate, SS5 dense discocytes show a greater increase in the percentage of granular cells than that observed for SS4 RBCs. Also, at a given deoxygenation rate, SS5 suspensions exhibit a higher viscosity than SS4 suspensions with fast deoxygenation resulting in maximal increase in viscosity. Although MCHC is the main determinant of SS RBC rheologic behavior, these studies demonstrate for the first time that at a given MCHC, the rate of deoxygenation (hence HbS polymerization rates) further modulates the rheologic behavior of SS RBCs. Thus, both MCHC and the deoxygenation rate may contribute to microcirculatory flow behavior of SS RBCs.     

Dehydration of transferrin receptor-positive sickle reticulocytes during continuous or cyclic deoxygenation: role of KCl cotransport and extracellular calcium

The K+ efflux that mediates sickle-cell dehydration may occur through several pathways, including two with a high capacity for mediating rapid K+ loss, KCl cotransport and the Ca(2+)-dependent K+ channel [K(Ca2+)]. The rate and pathway of red blood cell (RBC) dehydration most likely depends on cell age and hemoglobin (Hb) composition, with the presence of HbF playing an important role. Oxygenated sickle RBCs have relatively stable cell volume during incubation in vitro, whereas deoxygenated cells become dehydrated, and therefore more dense, due to activation of one or more K+ efflux pathways. In this investigation, sickle RBCs were deoxygenated either continuously or in 15-minute cycles for 4 hours, and the density increases of very young, transferrin receptor-positive (TfR+) cells and the remaining TfR- cells were determined. The contribution of KCl cotransport was estimated by replacing Cl- with NO3-. K(Ca2+) was inhibited by removal of Ca2+ or addition of charybdotoxin (ChTX). For both continuous and cyclic deoxygenation, TfR+ cells had a greater density increase when compared with TfR- cells. The lower percentage of HbF found in the TfR+ population may contribute to this difference. With continuous deoxygenation, the density shift was decreased by inhibition of K(Ca2+), but not by inhibition of KCl cotransport. With cyclic deoxygenation, the density shift was decreased in an independent, additive manner by inhibition of both pathways. Thus, cyclic deoxygenation of sickle cells under these conditions appears to activate both K(Ca2+) and the KCl cotransporter.     

Association between arterial stiffness and the deformability of red blood cells (RBCs)

The relationship between the flexibility of atherosclerotic vessels and RBC deformability has been investigated. A significant difference of RBC deformability was found among the arterial stiffness groups classified by oscillometric measurement of blood pressure. The deformability was determined by direct microscopic observation of RBCs subjected to shear stress of 0.3 to 40.0 Pa with a rotating rheoscope. The deformability of stiffen group - abnormal pulse wave pattern group or moderate cardiovascular risk group - was found to be much higher than that of normal groups in wide shear stress region (3.0, 10.0, 30.0, and 40.0 Pa). We postulate that the body adapts high shear stress in vivo by making RBCs more distensible, and therefore less likely to rupture under strain or microcirculatory alterations.     

Deformability characteristics of sickle cells by microelastimetry

Deformability of normal and sickle erythrocytes was measured by means of micropipette elastimetry with determination of intrinsic membrane rigidity (P) and total cell deformability (Pt). In the elastimetric technique employed, negative pressure at the pipette tip was generated and measured continuously. Membrane rigidity is defined as the negative pressure, in mm H₂O, required to induce a hemispherical projection of the cell surface into the micropipette, and total cell deformability as the negative pressure required to aspirate the entire cell into the pipette lumen. Membrane rigidity for oxygenated sickle discocytes was not statistically different from that of control normal discocytes, but Pt measurements were significantly higher for sickle than normal discocytes. Irreversibly sickled cells (ISCs) had markedly increased membrane rigidity and whole cell deformability when compared to control normal cells. Mildly deformed ISCs and severely deformed ISCs at ambient pO₂, both showed significantly higher mean membrane rigidity values than sickle discocytes and reversibly sickled cells. Sickle and normal discocytes both showed membrane elasticity with reversion to original cell shape following release of the cell from its aspirated position at the pipette tip. ISCs, however, exhibited elastic deformation of the membrane. These studies provide further evidence of progressive alteration of the sickle cell membrane induced by the sickling-unsickling process, culminating in formation of the ISC, and suggest a role for the ISC membrane abnormality in the pathologic rheology of sickle cell disease.     

Clinical and laboratory factors associated with the severity of proliferative sickle cell retinopathy in patients with sickle cell hemoglobin C (SC) and homozygous sickle cell (SS) disease

Proliferative sickle cell retinopathy (PSCR) is the most frequent vision-threatening complication of sickle cell disease (SCD). We investigated the relationship between the severity of sickle cell retinopathy in heterozygous (SC) or homozygous (SS) adult SCD patients and the clinical and laboratory data obtained during visits to a national SCD referral center. This retrospective longitudinal analysis included 942 SCD patients (313 patients with SC and 629 with SS disease) with ophthalmologic evaluations who were followed over a 19-year period by a multidisciplinary team in a referral center. PSCR was graded using the Goldberg classification. We identified patient and SCD characteristics associated with sickle cell retinopathy severity using multinomial logistic-regression models. Multivariate analysis associated severe PSCR forms (stages III-V) with older age (p=0.032), pulmonary involvement (documented pulmonary hypertension with pulmonary arterial pressure≥40 mm Hg, restrictive syndrome>20%, or previous history of pulmonary embolism diagnosed by vascular imaging) (p=0.029), deafness or tinnitus (p=0.026), and no history of osteomyelitis (p=0.013) for SC patients; and with older age (p<0.001), male sex (p=0.003), and acute pyelonephritis (p=0.04) for SS patients. The model of severe PSCR versus no PSCR showed good calibration and discrimination for SC and SS patients. Awareness of the clinical and laboratory factors significantly associated with severe PSCR in patients with SC or SS SCD may contribute to improved preventive strategies.     

New insights provided by a comparison of impaired deformability with erythrocyte oxidative stress for sickle cell disease

Sickle cell disease (SCD) is associated with increase in oxidative stress and irreversible membrane changes that originates from the instability and polymerization of deoxygenated hemoglobin S (HbS). The relationship between erythrocyte membrane changes as assessed by a decrease in deformability and oxidative stress as assessed by an increase in heme degradation was investigated. The erythrocyte deformability and heme degradation for 27 subjects with SCD and 7 with sickle trait were compared with normal healthy adults. Changes in both deformability and heme degradation increased in the order of control to trait to non-crisis SCD to crisis SCD resulting in a very significantly negative correlation between deformability and heme degradation. However, a quantitative analysis of the changes in deformability and heme degradation for these different groups of subjects indicated that sickle trait had a much smaller effect on deformability than on heme degradation, while crisis affects deformability to a greater extent than heme degradation. These findings provide insights into the relative contributions of erythrocyte oxidative stress and membrane damage during the progression of SCD providing a better understanding of the pathophysiology of SCD.     

Inhibition of tissue damage by the arachidonate lipoxygenase inhibitor BW755C.

The effects of three anti-inflammatory drugs, which interfere with arachidonic acid transformation by three different enzymes, have been compared by using a simple model of tissue damage and foreign body rejection. In groups of control rats, subcutaneously implanted polyester sponges were rejected after a mean of 12 days. Indomethacin, which selectively inhibits prostaglandin synthesis, did not significantly change time to rejection but BW755C (3-amino-1-[m-(trifluoromethyl) phenyl]-2-pyrazoline), which is a dual inhibitor of prostaglandin and leukotriene synthesis, prolonged time to rejection to a mean of 22 days. The anti-inflammatory steroid dexamethasone, which reduces arachidonic acid metabolism by stimulating the formation of a phospholipase inhibitor, prolonged time to sponge rejection as BW755C did. Treatment with BW755C or dexamethasone was also accompanied by a reduction in total leukocyte numbers in inflammatory exudates collected at 1-14 days, whereas indomethacin increased leukocyte migration on days 1 and 2 and had no effect at later times. These results suggest that the inhibition of the leukotriene-forming lipoxygenase suppresses leukocyte activation and that this leads to a reduced rate of tissue damage in experimental inflammation.     

Serum unsaturated vitamin B12 proteins in adult patients with sickle cell anaemia (HbSS)

The unsaturated vitamin B12 binding capacity (UBBC) of serum, the three transcobalamins (TC I, TC II, TC III) and serum cobalamin have been studied in adult sickle cell patients with Hb SS. An increase in the level of the binding capacities of TC I and TC III resulting in an increase in UBBC was observed in these patients. There was no difference in the level of the binding capacity of TC II, while there was a significant reduction in the level of serum cobalamin. These changes in the pattern of these binding proteins are discussed in relation to the changes of these binding proteins in paediatric sickle cell patients with Hb SS. The results indicate that the pattern of these binding proteins changes with age among sickle cell patients resulting in an increased level of the binding capacities of TC I and TC III. These increases lend support to the view that these two similar binding proteins are involved in the defence mechanism of the body.     

Life-threatening thrombotic thrombocytopenic purpura (TTP) in a patient with sickle cell-hemoglobin C disease

We report a patient with hemoglobin sickle cell-hemoglobin C disease who developed the clinical syndrome of thrombotic thrombocytopenic purpura (TTP) during admission for typical acute pain crisis. The potential for multiorgan involvement secondary to vaso-occlusive crisis complicated the diagnosis and overlapped with the patient's clinical presentation of chronic bone pain and hemolytic anemia. Clinical improvement and normalization of laboratory parameters followed rapidly in response to plasma exchange therapy.     

格列喹酮可促进成肌细胞葡萄糖摄取

目的 观察格列喹酮对小鼠成肌细胞(C2C12)葡萄糖摄取及葡萄糖转运相关蛋白葡萄糖转运体4表达的影响.方法 采用格列喹酮干预体外培养的C2C12细胞,将细胞分为空白组、胰岛素组(1×10-7mol/L胰岛素)、格列喹酮组(1×10-5mol/L格列喹酮)、格列喹酮+胰岛素组(1×10-5mol/L格列喹酮+1×10-7mol/L胰岛素).应用葡萄糖氧化酶法检测细胞培养基中葡萄糖水平,DMEM组葡萄糖含量平均值减去其余各孔葡萄糖含量算得各孔细胞葡萄糖消耗量;用MTT法检测细胞活力;利用液闪计数法检测C2C12细胞葡萄糖摄取量;采用半定量实时聚合酶链反应(RTPCR)检测细胞中葡萄糖转运体4 mRNA水平.应用单因素方差分析进行数据统计.结果 与空白组相比,格列喹酮组C2C12细胞葡萄糖消耗量明显增加[(11.0±0.5)vs(7.9±0.6)mmol/L,q=0.36,P＜0.01];格列喹酮+胰岛素组C2C12细胞葡萄糖消耗量较胰岛素组增多[(13.8±0.7)vs(12.3±0.6)mmol/L,q=0.72,P＜0.01].胰岛素组、格列喹酮组C2C12细胞对葡萄糖的摄取均增加,分别为空白组的(1.68±0.09)、(1.52±0.23)、(1.23±0.16)倍(q值分别为14.78、11.30、5.00,均P＜0.01);格列喹酮组C2C12细胞葡萄糖摄取增加较格列苯脲组明显(q=6.30,P＜0.01),格列喹酮+胰岛素组C2C12细胞葡萄糖摄取为空白组的(1.93±0.12)倍(q=13.04,P＜0.01),且明显高于胰岛素组(q=5.43,P＜0.01).格列喹酮组C2C12细胞葡萄糖转运体4 mRNA水平与空白组比较无明显差异.结论 格列喹酮可促进C2C12细胞对葡萄糖的摄取,增加胰岛素刺激的葡萄糖摄取,并未增加C2C12细胞葡萄糖转运体4基因表达.     

Natriuretic peptides suppress protein kinase C activity to reduce evoked dopamine efflux from pheochromocytoma (PC12) cells

The observation that natriuretic peptides and protein kinase C activators influence evoked neurotransmitter efflux by diametrically opposed mechanisms prompted an investigation of the influence of natriuretic peptides on protein kinase C activity and the potential involvement of this pathway in neuromodulatory responses to natriuretic peptides. C-Type natriuretic peptide attenuated both evoked dopamine efflux and protein kinase C activity in a concentration-dependent manner consistent with a 10% diminution in protein kinase C activity producing a 4.6-6.2% reduction in evoked dopamine efflux. The ability of C-type natriuretic peptide to suppress evoked dopamine efflux was abolished by treatment with the protein kinase C inhibitors chelerythrine (10 micro M) and staurosporine (10 nM). Both chelerythrine and staurosporine attenuated protein kinase C activity at the concentrations used. The natriuretic peptide C receptor (NPR-C) appeared to mediate the attenuation of protein kinase C activity, because the effect was mimicked by a pentadecapeptide fragment of the NPR-C, and the effect of C-type natriuretic peptide was attenuated by an antibody generated against the same region of the receptor. These data suggest that C-type natriuretic peptide attenuates neurotransmitter efflux by a mechanism involving suppression of neuronal protein kinase C activity via an interaction with the NPR-C.     

Vaso-occlusion by sickle cells: evidence for selective trapping of dense red cells

We have characterized the type of red cells from sickle cell patients that were trapped in the course of sickle-cell vaso-occlusion. In addition, the perfusion conditions (arterial perfusion pressure [Pa] and oxygen tension [PO2]) leading to experimentally induced vaso-occlusion in the artificially perfused, innervated mesocecum microvascular preparation were determined. Microvascular obstruction was induced by decrease in Pa; the lower the Pa, the greater the peripheral resistance as well as the extent of obstruction. The cells involved in the obstruction were recovered by vasodilation (secondary to denervation) and increase in Pa. Densitometric analysis of density gradient-separated infused and trapped cells was supplemented with morphological analysis to ascertain the involvement of density classes as well as morphological types seen in oxy and deoxy sickle blood. The trapping phenomenon was sensitive to PO2. Percentage of densest gradient classes, ie, fraction 3 (F3; mainly dense unsicklable SS discocytes [USDs]) and fraction 4 (F4; irreversibly sickled cells [ISCs] and the densest discocytes), showed a significant increase in trapping when perfusion was switched from oxy to deoxy perfusate. Morphological analysis revealed that unsicklable SS discocytes are more effectively trapped when deoxygenated. The deoxygenation of infused cells did not further change the percentage of ISCs trapped, suggesting that ISCs are equally capable of sequestration in the oxy and the deoxy states. The venous effluent showed a selective and significant depletion of dense cells (F4) and ISC counts at all Pa. We conclude that the progressive obstruction of the microcirculation by sickle cells involves selective sequestration of the densest classes of cells and that this mechanism might explain their partial disappearance during painful sickle cell crisis.     

No decreased erythrocyte deformability in type 1 (insulin-dependent) diabetes,either by filtration or by ektacytometry

A lower erythrocyte deformability, which causes impairment of the microcirculation, is postulated to contribute to diabetic organ complications. Erythrocyte deformability was measured in four groups of type 1 (insulin-dependent) diabetic subjects and 30 controls by filtration and ektacytometry. Twenty-five patients without overt nephropathy and 12 with leg ulceration were studied. No decreased erythrocyte deformability was found in any of the diabetic groups with either technique, and neither did the total group of 71 diabetic subjects have a lower erythrocyte deformability when compared with the controls. In order to imitate local conditions in the kidney, erythrocyte deformability was also measured in hyperosmolar solutions. Again no differences were found between the diabetic groups separately or as a whole and the controls. Furthermore no correlation was found between erythrocyte deformability and the plasma glucose or glycosylated haemoglobin level.